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Cloud seeding is a fairly common practice in most of the world; the aim is to introduce a nucleus into a cloudbank around which supercooled water in the cloud can condense and form precipitation. It’s been practiced in various forms since 1946, but has always remained somewhat controversial since it is impossible to know if the seeding had any effect, or if it was going to rain anyhow.
In 1962 the US took cloud seeding to the next level by embarking upon Operation Stormfury. The idea was to effect weather’s most powerful event: the hurricane. After Bernard Vonnegut discovered the effectiveness of silver iodine in cloud seeding it was decided to try to seed a hurricane. The models of the time predicted that the eyewall of a hurricane contained large amounts of supercooled water, and that seeding the eyewall would result in the atmospheric water becoming precipitation, falling out, and thus robbing the hurricane of some of its most potent and concentrated fury, cause the rest of the hurricane to shrink inward to make up for the destabilization, and surrender some of the circular energy.
By the time the project ended in the millions of dollars and twenty years later, they’d learned a great deal about the mechanisms in hurricane that allowed for better tracking and power predictions, but the attempts to reduce them were unsuccessful. It was determined that there was not as much supercooled water in the eyewall as the initial projections, and since seeding is unproven anyhow, it was impossible to tell if it was having any effect.